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From: Bart Van Assche <bvanassche@acm.org>
To: dgilbert@interlog.com,
	SCSI development list <linux-scsi@vger.kernel.org>,
	"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>
Cc: "Martin K. Petersen" <martin.petersen@ORACLE.COM>,
	USB list <linux-usb@vger.kernel.org>
Subject: Re: lib/scatterlist.c : sgl_alloc_order promises more than it delivers
Date: Fri, 25 Sep 2020 21:32:43 -0700	[thread overview]
Message-ID: <da346d8f-b27e-7880-10e8-f2617e0ec7ff@acm.org> (raw)
In-Reply-To: <d487005a-ef6c-549f-7006-c7056cf3f36d@interlog.com>

On 2020-09-24 21:55, Douglas Gilbert wrote:
> My code steps down from 1024 KiB elements on failure to 512 KiB and if that
> fails it tries 256 KiB. Then it gives up. The log output is consistent with
> my analysis. So your stated equality is an inequality when length >= 4 GiB.
> There is no promotion of unsigned int nent to uint64_t .
> 
> You can write your own test harness if you don't believe me. The test machine
> doesn't need much ram. Without the call to sgl_free() corrected, if it really
> did try to get that much ram and failed toward the end, then (partially)
> freed up what it had obtained, then you would see a huge memory leak ...> 
> 
> Now your intention seems to be that a 4 GiB sgl should be valid. Correct?
> Can that check just be dropped?

Hi Doug,

When I wrote that code, I did not expect that anyone would try to allocate
4 GiB or more as a single scatterlist. Are there any use cases for which a
4 GiB scatterlist works better than two or more smaller scatterlists?

Do you agree that many hardware DMA engines do not support transferring
4 GiB or more at once?

Thanks,

Bart.

  reply	other threads:[~2020-09-26  4:32 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-25  1:46 lib/scatterlist.c : sgl_alloc_order promises more than it delivers Douglas Gilbert
2020-09-25  2:34 ` Bart Van Assche
2020-09-25  4:55   ` Douglas Gilbert
2020-09-26  4:32     ` Bart Van Assche [this message]
2020-10-11 21:21       ` Douglas Gilbert
2020-10-11 22:24         ` Bart Van Assche

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